A common case is that one constructs a grouping variable in group_by but only needs it for the duration of the group_by so afterwards one must use select to get rid of it as in the example below. It would be pleasingly symmetric if ungroup could remove the added column just as group_by adds it so
would be the same as
Thus in this example taken from https://stackoverflow.com/questions/51939874/referencing-previous-column-value-as-column-is-created/51940343#51940343
test <- structure(list(i = c(0, 1, 2, 3, 4, 0, 1, 2, 3, 4), chng = c(0,
0.031, 0.005, -0.005, 0.017, 0, 0.012, 0.003, -0.013, -0.005),
indx = c(1, 1.031, 1.037, 1.031, 1.048, 1, 1.012, 1.015,
1.002, 0.997)), class = "data.frame", row.names = c(NA, -10L
))
test %>%
group_by(g = cumsum(i == 0)) %>%
mutate(indx = cumprod(chng + 1)) %>%
ungroup %>%
select(-g)
we could write using one fewer statement, i.e. the last two lines of code above are combined into the last line below.
test %>%
group_by(g = cumsum(i == 0)) %>%
mutate(indx = cumprod(chng + 1)) %>%
ungroup(-g)
Note the reduced line count and improved symmetry.
j450h1, maxmoro, calebbraun and djbirke
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